When moving out of a for loop head, suggest borrowing it

When encountering code like the following, suggest borrowing the for loop
head to avoid moving it into the for loop pattern:

```
fn main() {
    let a = vec![1, 2, 3];
    for i in &a {
        for j in a {
            println!("{} * {} = {}", i, j, i * j);
        }
    }
}
```

2 files changed, 34 insertions, 0 deletions

diff --git a/src/test/ui/suggestions/borrow-for-loop-head.rs b/src/test/ui/suggestions/borrow-for-loop-head.rs
new file mode 100644
index 00000000000..c2bda55e589
--- /dev/null
+++ b/src/test/ui/suggestions/borrow-for-loop-head.rs
@@ -0,0 +1,10 @@
+fn main() {
+    let a = vec![1, 2, 3];
+    for i in &a {
+        for j in a {
+        //~^ ERROR cannot move out of `a` because it is borrowed
+        //~| ERROR use of moved value: `a`
+            println!("{} * {} = {}", i, j, i * j);
+        }
+    }
+}
diff --git a/src/test/ui/suggestions/borrow-for-loop-head.stderr b/src/test/ui/suggestions/borrow-for-loop-head.stderr
new file mode 100644
index 00000000000..17ac3fe86d0
--- /dev/null
+++ b/src/test/ui/suggestions/borrow-for-loop-head.stderr
@@ -0,0 +1,24 @@
+error[E0505]: cannot move out of `a` because it is borrowed
+  --> $DIR/borrow-for-loop-head.rs:4:18
+   |
+LL |     for i in &a {
+   |               - borrow of `a` occurs here
+LL |         for j in a {
+   |                  ^ move out of `a` occurs here
+
+error[E0382]: use of moved value: `a`
+  --> $DIR/borrow-for-loop-head.rs:4:18
+   |
+LL |         for j in a {
+   |                  ^ value moved here in previous iteration of loop
+   |
+   = note: move occurs because `a` has type `std::vec::Vec<i32>`, which does not implement the `Copy` trait
+help: consider borrowing this to avoid moving it into the for loop
+   |
+LL |         for j in &a {
+   |                  ^^
+
+error: aborting due to 2 previous errors
+
+Some errors occurred: E0382, E0505.
+For more information about an error, try `rustc --explain E0382`.